Okay so this is really the first challenge I have tried to create. I don't know if others have tried this or not, this is just what I have done.

The Farm Challenge

So you must create a young adult/adult Sim in CAS to start this challenge. I created a young woman and I kept things simple with her, no jewelry, make-up and no shoes.
This Sim must have the Freelance Botanist as their main trait and loves the outdoor as the second. The other two are up to you.

So to start you must create a house with all the basics to live on. As well as plenty of dirt for gardening, 6 plant boxes and 3 garden pots. As well as 2 outdoor flora that improves the environment. As well as a woodworking bench for extra funds. You must spend most of the money you start with but leave enough to buy 2 each of the starter seeds.

The Goals:
To live of the land. You may not have a job outside the home. The only way you can make money is through selling your crop. Selling your wood sculptures, or things that you find while outside and in the community. You can travel anywhere and collect things and sell them.

So you start out you must fill all the plant boxes with edible plants(vegetables, fruits and herbs) No tree plants though, apples and plantains.
Those as well as flowers must be planted in dirt, not grass. You choose the soil as well, those can be found in build mode, paint terrain.

You must keep your plants alive and can only have three that die and have to be thrown away. As you go along your gardening skill will increase as well as meeting goals for your Freelance Botany Aspiration. As you go along you can resurrect a dead plant and may do so if need be. You must also take cuttings from 5 different plants and graft them to other plants. Trying to create new plants.

Along the way you must fall in love and get married.(Just a note once you start romancing, you will need to buy a double bed) Or you cannot have that person stay the night. They must also move in before you wed. Your partner can be male/female, but you must have at least one child together. Gay couples must adopt a baby and straight couples must have a child. Once they move in money they bring in must be spent on making the home nicer and better. You must save 2,000 of that to have a wedding party. The wedding is 1,000 dollars and the other is to either adopt or spend on a new child. You also may make money at any time during this challenge by selling your crop. So having some extra money is always good especially because at the wedding you may have to pay for drinks, or staff to help out.

Once your spouse is a part of your life, their aspiration much be changed to freelance botanist as well to help with the crops. You and your spouse must work together to make the farm a success.

To complete the challenge,Your original Sim must reach the highest level in gardening, as well as complete their freelance botanist aspiration. Must have 5,000 in household funds from living off the land. As well as raise a child and pass the farm to them.

I do this challenge all the time

Same here with the exception that I allows trees too.
It works better with multiple sims, the cost for 2-3 is not much higher than one and it help doing the work, you can fish and collect rocks on the side.
The income for some of the high level harvests is very good,